1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, an LCD device having an electromagnetic (EM) sensor for preventing a mistake in a location detection, in which a lamp housing is formed first of a flexible material, and a supplementary lamp housing is formed to support the flexible lamp housing at a lamp side except a light-guiding plate.
2. Discussion of the Related Art
In a personal information processor such as a personal computer and a mobile transmission device, various input devices such as a keyboard, a mouse and a digitizer have been generally used for text and graphic processing. Because the personal computer is used in various fields, it is necessary to replace input devices such as the keyboard and the mouse with a touch panel due to demands for mobility and simplicity, whereby a user can input information such as letters on the touch panel while carrying the same. The touch panel has been developed from a device satisfying a general input function to a high-technology device having reliability and long life.
A touch panel is known as an input device having simplicity, mobility, operation reliability and letter input functionality. Capable of sensing when a user touches a display surface, touch panels are classified as resistive type, capacitive type, and an electromagnetic (EM) type. The resistive type touch panel detects a location of a touching point by pressure while applying a D.C. voltage in accordance with a change of capacity. The capacitive type touch panel detects a location of a touching point by using Capacitance Coupling while applying an A.C. voltage. Also, the EM type touch panel detects a location of a touching point by detecting a resonance frequency resonated as an induced voltage while applying an electromagnetic field. Each type of touch panel has signal amplification problems, resolutions and development difficulty. Various optical, electrical, mechanical and input characteristics as well as endurance and cost are considered as criteria for choosing a particular type of touch panel. Recently, the EM type touch panel has attracted great attention.
The LCD device does not emit light in itself. That is, the LCD device displays a picture image by controlling light transmittance from an external source. Thus, the LCD device requires an additional light source such as a backlight. At this time, the LCD device uses a light source such as an Electro Luminescence (EL), a Light Emitting Diode (LED), a Cold Cathode Fluorescent Lamp (CCFL) or a Hot Cathode Fluorescent Lamp (HCFL). The CCFL has a long lifetime, low power consumption and thin profile and is used as the light source for large-sized color TFT LCD devices.
In the case of the cold cathode fluorescent lamp (CCFL), a fluorescent discharge tube is used for a penning effect, which is formed by injecting a hydrargyrum Hg gas containing Argon Ar and Neon Ne at a low temperature. Also, electrodes are formed at both ends of the fluorescent discharge tube, and the cathode is formed in a plate-shape. When a voltage is applied to the discharge tube, electric charges inside the fluorescent discharge tube collide against the plate-shaped cathode in a sputtering state, thereby generating secondary electrons. Thus, circumferential elements are excited by the secondary electrons, and plasma is generated. Also, the circumferential elements emit strong ultraviolet rays. The ultraviolet rays excite a fluorescent substance and thereby emit visible rays.
The backlight may be classified as a direct-type and an edge-type based upon the position of a lamp unit.
In the edge-type method, a lamp unit is formed at one side of a light-guiding plate. The lamp unit includes a lamp, a lamp holder and a lamp reflecting plate. The lamps, emitting light, are inserted into both sides of the lamp holder, whereby the lamp is protected from an external impact. Also, the lamp reflecting plate surrounds a circumferential surface of the lamp, and one side of the lamp reflecting plate is inserted to one side of the light-guiding plate to reflect the light emitted from the lamp to the light-guiding plate. Generally, the edge-type method of forming the lamp unit at the one side of the light-guiding plate is applied to relatively small-sized LCD devices such as monitors for laptop type computers or desktop type computers. The edge-type method is useful to obtain uniform luminance, long lifetime and thin profile in the LCD device.
With the trend of the large-sized LCD devices of 20-inch or more, the direct-type method is being actively developed. With the direct-type method, a plurality of lamps are formed in one line on a lower surface of a light-diffusion plate, whereby the entire surface of the LCD panel is directly illuminated with the light. The direct-type method, which has greater light efficiency as compared with that of the edge-type method, is used for large-sized LCD devices that require high luminance. That is, the LCD devices of the direct-type method are generally used for a large-sized monitor or the television. The large-sized monitor or the television may be driven for a long time, and has a plurality of lamps, whereby it tends to have the lamps being turned off. However, in the LCD device of the edge-type method having lamp units at both sides of the light-guiding plate, it does not cause big problems except the decrease of the luminance even though one lamp is turned off. Meanwhile, in the direct-type LCD device, a plurality of lamps are formed underneath a screen. Accordingly, if one of the lamps is turned off due to troubles with the lamp or the end of the lamp life, a screen portion corresponding to the turned-off lamp portion becomes darker as compared with surrounding portions of the screen. In this respect, the direct-type LCD device has to have a simple structure suitable for disassembly and assembly of the lamp unit.
Hereinafter, a LCD device having the edge-type backlight and the EM sensor according to the related art will be described with reference to the accompanying drawings.
FIG. 1 illustrates a structure of a general backlight assembly. As shown in FIG. 1, the general backlight assembly is provided with a fluorescent lamp 1, a light-guiding plate 2, a light-diffusion substance 3, a reflecting plate 4, a light-diffusion plate 5 and a prism sheet 6. When a voltage is applied to the fluorescent lamp 1, electrons remaining in the fluorescent lamp 1 move to the anode, and the remaining electrons collide with argon Ar, whereby the argon Ar is excited. As a result, positive ions are generated, and the positive ions collide against the cathode, thereby generating secondary electrons. When the secondary electrons are discharged to the fluorescent lamp 1, the flow of the electrons collides with hydrargyrum vapor, and then ionized, thereby emitting ultraviolet rays and visible rays. Then, the emitted ultraviolet rays excite a fluorescent substance deposited inside the fluorescent lamp, thereby emitting light.
Subsequently, the light-guiding plate 2 is a Light Wave-Guide causing the light emitted from the fluorescent lamp 1 to be incident on the LCD, as a plate type light source. The light-guiding plate 2 may be formed of Poly Methyl Meth Acrylate (PMMA) resin having a great light transmittance. The light incidence of the light-guiding plate 2 is related to the ratio between the light-guiding plate thickness and the fluorescent lamp diameter, the distance between the light-guiding plate and the fluorescent lamp 1, and the shape of the reflecting plate. Generally, the fluorescent lamp 1 is slanted on the center of the light-guiding plate 2 at the thickness direction, thereby improving efficiency of the light incidence. The light-guiding plate 2 for the backlight unit of the LCD device is divided into a printing-type light-guiding plate, a V-cut type light-guiding plate, and a scattering-type light-guiding plate.
Next, a light-diffusion substance 3 may include SiO2 particles, PMMA and solvent. At this time, SiO2 particles having porosity are used for diffusing the light. Also, PMMA is used for adhering SiO2 particles to a lower surface of the light-guiding plate 2. The light-diffusion substance 3 is deposited on the lower surface of the light-guiding plate 2 in dotted patterns, and the sizes of the dotted patterns are gradually increased to obtain a uniform plate-type light source on an upper surface of the light-guiding plate 2. That is, the dotted pattern has a small size in a unit area near to the fluorescent lamp 1, and the dotted pattern has a large size in a unit area away from the fluorescent lamp 1. The shape of the dotted pattern may be varied. In the case of the dotted patterns having the same size, the respective dotted patterns have the luminance of the same level regardless of the dotted shape.
Subsequently, the reflecting plate 4 is formed at the rear of the light-guiding plate 2, whereby the light emitted from the light guiding plate 2 is reflected back inside of the light-guiding plate 2. Also, the light-diffusion plate 5 is formed on the upper surface of the light-guiding plate 2 to obtain a uniform luminance at each viewing angle. The light-diffusion plate 5 may be formed of PET or Poly Carbonate (PC) resin, and a particle-coating layer is formed on the light-diffusion plate 5 for diffusing the light.
Next, the prism sheet 6 is formed to improve the frontal luminance of the light transmitted and reflected to the upper side of the light-diffusion plate 5. The prism sheet 6 transmits the light of a predetermined angle, and the light incident at the other angles is totally reflected, whereby the light is reflected to the lower side of the prism sheet 6 by the reflecting plate 4 formed on the lower side of the light-guiding plate 2. The backlight assembly having the aforementioned structure is fixed to a mold frame, and a display unit disposed at an upper side of the backlight assembly is protected by a top sash. Also, the backlight assembly and the display unit are received between the top sash and the mold frame being coupled to each other.
FIG. 2 is a cross-sectional view illustrating an LCD device having an EM sensor according to the related art. As shown in FIG. 2, the LCD device includes a fluorescent lamp 11, a lamp housing 12, a light-guiding plate 13, a reflecting plate 14, a light-diffusion plate 15, a prism sheet 16, a protection sheet 17, and a main supporter 18. At this time, a fluorescent substance is coated inside the fluorescent lamp 11 for emitting light. Also, the lamp housing 12 fixes the fluorescent lamp 11, and concentrates the light emitted from the fluorescent lamp 11 in one direction. The light-guiding plate 13 provides the light emitted from the fluorescent lamp 11 to an upper side of an LCD panel, and the reflecting plate 14 adheres to a lower side of the light-guiding plate 13 to reflect the light leaking in an opposite side of the LCD panel to the light-guiding plate 13. The light-diffusion plate 15 is formed on an upper side of the light-guiding plate 13 to uniformly diffuse the light emitted from the light-guiding plate 13. Also, the prism sheet 16 is formed on an upper side of the light-diffusion plate 15 to concentrate the light diffused in the light-diffusion plate 15, and to transmit the concentrated light to the LCD panel, and the protection sheet 17 is formed on an upper side of the prism sheet 16 to protect the prism sheet 16. The main supporter 18 receives and fixes the aforementioned elements.
In the aforementioned backlight unit, the light emitted from the fluorescent lamp 11 is concentrated on an incident surface of the light-guiding plate 13, and then the concentrated light passes through the light-guiding plate 13, the light-diffusion plate 15 and the prism sheet 16, whereby the light is transmitted to the LCD panel 10. Also, an EM sensor 19 serving as an EM type touch panel is provided below the lamp housing 12 of aluminum Al material. That is, the EM sensor is overlapped with the lamp housing 12. At this time, in region B serving as an effective region of the EM sensor, mistakes may be generated in detecting the location of the touching point since the lamp housing 12 prevents electromagnetic transmission between the EM sensor 19 and an electronic (stylus) pen 7. In this case, a region A is not an effective region in the LCD panel 10, but the region A is an effective region in the EM sensor 19. A region B indicates a portion of the lamp housing 12 in the effective region of the EM sensor 19. A region C indicates a portion of the light-guiding plate in the non-effective region of the EM sensor 19.
Hereinafter, a structure and an operation of the EM sensor 19 will be described as follows.
In a general EM type touch panel, the EM sensor 19 is formed as a plate which includes two sets of array coils (or coils), one set being perpendicular to the other set. In the structure of the plate type coil, a plurality of coils are piled on a flexible PCB (flexible Printed Circuit Board), and each coil is formed for being apart from X-axis and Y-axis. Also, one end of each coil is connected to a ground voltage, and the other end is connected to one common reference electric potential line receiving a selective signal.
In a system having the EM sensor in the backlight, when the electronic (stylus) pen having a resonant circuit is positioned on the LCD panel, the EM sensor is driven by a D.C. signal to generate a resonant magnetic field. Then, the magnetic field induces a signal to the array coil. The signal induced to the array coil is detected by the controller below the backlight unit, and then compared, so that the location of the touching point is detected on the plate two-dimensionally.
The EM sensor 19 includes the plurality of coils, and the coils are formed of a conductive material having light-shielding characteristics. As a result, it is possible to prevent a decrease of light transmittance by positioning the EM sensor below the reflecting plate 14 of the backlight unit. The resistive type or capacitive type touch panel has to be mounted on the display device to detect the location of the touching point. However, in the case of the EM type touch panel, the sensor may be apart from the display surface, which is touched by a user, for detecting the location of the touching point because the electromagnetic force is transmitted through the display device and light source.
However, the LCD device having the EM sensor according to the related art has the following disadvantages.
The lamp housing that concentrates the light emitted from the lamp is formed of aluminum Al. Thus, at a portion where the lamp housing is overlapped with the EM sensor, mistakes may be generated in detecting the location of the touching point because the lamp housing prevents electromagnetic transmission between the EM sensor and the electronic (stylus) pen.